The present invention relates to telecommunications in general, and, more particularly, to an IEEE 802.11 wireless local area network.
FIG. 1 depicts a schematic diagram of a portion of wireless telecommunication system 100 in the prior art, which comprises stations 101-1 through 101-5 and access point 102. Stations 101-1 through 101-5 and access point 102 can communicate with each other within shared communications network 103 and with wired backbone network 104 via access point 102. Stations 101-1 through 101-5 and access point 102 constitute an IEEE 802.11(a) or 802.11(b) wireless local area network (hereinafter also called a xe2x80x9cWLANxe2x80x9d). An IEEE 802.11(b) network is also known as a xe2x80x9cWi-Fixe2x80x9d network.
Stations 101-1 through 101-5 are computing devices capable of communicating with each other using wireless network interfaces and, together, constitute a basic service set (hereinafter also called a xe2x80x9cBSSxe2x80x9d). A basic service set can be regarded as a building block for an 802.11-based network. Access point 102 enables stations 101-1 through 101-5 to communicate with the rest of the world via wired backbone network 104. Stations 101-1 through 101-5 and access point 102 communicate with each other through a wireless medium, which is depicted as shared communications network 103.
Wireless telecommunication system 100 is classified as an infrastructure BSS because it comprises an access point. An infrastructure BSS is contrasted with an independent BSS, or IBSS, which does not comprise an access point. In wireless telecommunication system 100, access point 102 is involved in all communications, including those in which two stations (e.g., stations 101-1 and 101-5, etc.) communicate with each other. This is because the infrastructure BSS has a logical star topology, and, therefore, access point 102 relays all communications between stations in the BSS.
Referring to FIG. 2A, if station 101-1 wishes to send, for example, a data frame to station 101-5, station 101-1 first sends data frame 201 to access point 102. Access point 102 then attempts to relay data frame 201 to access point 102. To accomplish this, access point 102 first checks to see if station 101-5 is in active mode, and, therefore, is ready to receive the relayed frame. Station 101-5 might, however, be in power save mode, and, therefore, not ready to receive the relayed frame.
When a station is in power save mode, the station has placed its transmitter and receiver in a low power state to conserve power, and, therefore cannot transmit or receive. In accordance with a predictable schedule, a station in power save mode powers up its receiver periodically to determine if the access point has any frames waiting for it. The access point knows when the stations in its BSS wake up from power save mode and initiates a message transaction. Referring again to FIG. 2A, in message transaction 202, access point 102 transmits a beacon frame that comprises a traffic indication map. Station 101-5 then transmits a PS-Poll frame, requesting that the frame be sent. Access point 102 then forwards the data frame to station 101-5. Additional frames from station 101-1 through access point 102 can follow.
Similarly, station 101-5 might have one or more data frames to send back to station 101-1, which is depicted in FIG. 2B. Station 101-5 transmits data frame 203. Access point 102 then initiates message transaction 204 with station 101-1, and delivers the data frames.
Direct communication between stations 101-1 and 101-5 is often desirable, but it is problematic because a transmitting station would not know if an intended receiving station were in power save mode and, therefore, unable to receive frames.
The present invention provides a technique that enables a first 802.11 enhanced station to communicate with a second 802.11 enhanced station directly, even when the second station periodically or sporadically enters power save mode. Furthermore, enhanced stations such as those in the illustrative embodiment are backwards compatible, and, therefore, can operate in a basic service set comprising legacy stations.
In accordance with the illustrative embodiment of the present invention, an enhanced station, hereinafter called a Q-station, requests a direct link with another Q-station (i.e., the targeted Q-station) by first transmitting a direct_link_protocol_request frame to an access point. The access point and not the requesting Q-station then determines if the targeted Q-station is in power save mode. If the targeted Q-station is in power save mode, the access point xe2x80x9cwakesxe2x80x9d the Q-station by transmitting a beacon frame that comprises a traffic indication map. This wakes the targeted Q-station and causes it to respond by transmitting back to the access point a PS-Poll frame. When the access point receives the PS-Poll frame, the access point responds by forwarding the direct_link_protocol_request frame from the requesting Q-station to the targeted Q-station.
The targeted Q-station then responds by transmitting back a direct_link_protocol_response frame to the requesting Q-station, either through the access point or directly. The targeted Q-station then knows to expect a frame directly from the requesting Q-station. That frame might be, for example, a direct_link_protocol_probe frame to test the suitability of the direct link or a data frame.
The illustrative embodiment of the present invention comprises: receiving at an access point from a first Q-station a direct_link_protocol_request frame that indicates a second Q-station as the destination of the direct_link_protocol_request frame; transmitting from the access point a traffic indication map that indicates that traffic is available for the second Q-station; receiving at the access point, in response to the transmission of the traffic indication map, a PS-Poll frame from the second Q-station; and forwarding from the access point, in response to the reception of the PS-Poll frame, the direct_link_protocol_request frame to the second Q-station.